diff --git a/crates/switchyard-translation/src/codecs/responses/stream.rs b/crates/switchyard-translation/src/codecs/responses/stream.rs
index a179d4ee7..7776af9d1 100644
--- a/crates/switchyard-translation/src/codecs/responses/stream.rs
+++ b/crates/switchyard-translation/src/codecs/responses/stream.rs
@@ -355,7 +355,7 @@ fn encode_responses_stream(
                         .push_str(signature);
                 }
             }
-            match encrypted_reasoning_item_id(&details) {
+            match reasoning_details_item_id(&details) {
                 Some(id) if item.started && item.item_id.as_deref() != Some(id.as_str()) => {
                     // The item already opened under another id; the payload would fail
                     // verification under it, so drop the payload rather than poison the replay.
@@ -373,6 +373,13 @@ fn encode_responses_stream(
                     }
                 }
             }
+            // A summary that arrives before its item id would open the item under a synthesized
+            // id, and the encrypted payload that follows binds only to the provider's id. Hold
+            // the text until that id arrives, or until later output shows none is coming.
+            if !item.started && item.item_id.is_none() && summary_lacks_item_id(&details) {
+                item.pending_text.push_str(&text);
+                return ensure_responses_created(state);
+            }
             let mut out = ensure_responses_reasoning_started(state, index);
             if !text.is_empty() {
                 out.extend(encode_responses_reasoning_delta(state, index, text));
@@ -418,7 +425,8 @@ fn finish_responses_stream(state: &mut StreamTranslationState) -> Vec<Value> {
         ("response.completed", "completed")
     };
     let incomplete_details = is_truncated.then(|| json!({ "reason": "max_output_tokens" }));
-    let mut out = ensure_responses_created(state);
+    let mut out = open_held_reasoning(state, None);
+    out.extend(ensure_responses_created(state));
     if state.response_text_started
         && let Some(output_index) = state.response_text_output_index
     {
@@ -860,7 +868,8 @@ fn add_sequence_numbers(state: &mut StreamTranslationState, mut events: Vec<Valu
 
 // Accumulates assistant text and emits Responses text delta events.
 fn encode_responses_text_delta(state: &mut StreamTranslationState, text: String) -> Vec<Value> {
-    let mut out = ensure_responses_created(state);
+    let mut out = open_held_reasoning(state, None);
+    out.extend(ensure_responses_created(state));
     if !state.response_text_started {
         state.response_text_started = true;
         let output_index = state.next_response_output_index;
@@ -897,8 +906,65 @@ fn encode_responses_text_delta(state: &mut StreamTranslationState, text: String)
     out
 }
 
-// The id of the reasoning item encoded for a source index: the provider's own id when
-// encrypted reasoning binds to it, else synthesized from the emitted output index.
+// The provider item id named by a delta's reasoning details. The encrypted payload's id wins
+// because a replay verifies against it; a summary or text detail names the same item when it
+// arrives first.
+fn reasoning_details_item_id(details: &[Value]) -> Option<String> {
+    encrypted_reasoning_item_id(details).or_else(|| {
+        details
+            .iter()
+            .filter_map(Value::as_object)
+            .filter(|detail| {
+                matches!(
+                    detail.get("type").and_then(Value::as_str),
+                    Some("reasoning.summary" | "reasoning.text")
+                )
+            })
+            .find_map(|detail| {
+                detail
+                    .get("id")
+                    .and_then(Value::as_str)
+                    .filter(|id| !id.is_empty())
+            })
+            .map(ToOwned::to_owned)
+    })
+}
+
+// True when a `reasoning.summary` detail arrived without the id of the item it belongs to.
+fn summary_lacks_item_id(details: &[Value]) -> bool {
+    details.iter().filter_map(Value::as_object).any(|detail| {
+        detail.get("type").and_then(Value::as_str) == Some("reasoning.summary")
+            && detail
+                .get("id")
+                .and_then(Value::as_str)
+                .is_none_or(str::is_empty)
+    })
+}
+
+// Opens every reasoning item still holding summary text, under a synthesized id. Output that
+// is about to open another item proves no provider id is coming for them, and they must keep
+// their place ahead of it. When that output is itself a reasoning item, `before` limits the
+// flush to held items at earlier indices; the item's own later details can still name its id.
+fn open_held_reasoning(state: &mut StreamTranslationState, before: Option<usize>) -> Vec<Value> {
+    let held: Vec<usize> = state
+        .response_reasoning
+        .iter()
+        .filter(|(index, item)| {
+            before.is_none_or(|bound| **index < bound)
+                && !item.started
+                && !item.pending_text.is_empty()
+        })
+        .map(|(index, _)| *index)
+        .collect();
+    let mut out = Vec::new();
+    for index in held {
+        out.extend(ensure_responses_reasoning_started(state, index));
+    }
+    out
+}
+
+// The id of the reasoning item encoded for a source index: the provider's own id when a
+// reasoning detail named one, else synthesized from the emitted output index.
 fn responses_reasoning_item_id(state: &StreamTranslationState, index: usize) -> String {
     let item = state.response_reasoning.get(&index);
     item.and_then(|item| item.item_id.clone())
@@ -921,11 +987,14 @@ fn ensure_responses_reasoning_started(
     {
         return out;
     }
+    // Held summaries of earlier items open first, so they keep their place in the output.
+    out.extend(open_held_reasoning(state, Some(index)));
     let output_index = state.next_response_output_index;
     state.next_response_output_index += 1;
     let item = state.response_reasoning.entry(index).or_default();
     item.started = true;
     item.output_index = Some(output_index);
+    let pending = std::mem::take(&mut item.pending_text);
     let item_id = responses_reasoning_item_id(state, index);
     // Standard Responses shape: reasoning text lives in `summary` as `summary_text`
     // parts. Clients such as Codex record reasoning items only in this shape.
@@ -939,6 +1008,10 @@ fn ensure_responses_reasoning_started(
             "summary": [],
         },
     }));
+    // Summary text held for the item's id streams now, under the id it opened with.
+    if !pending.is_empty() {
+        out.extend(encode_responses_reasoning_delta(state, index, pending));
+    }
     out
 }
 
@@ -972,6 +1045,14 @@ fn encode_responses_reasoning_delta(
     index: usize,
     text: String,
 ) -> Vec<Value> {
+    // Text for an item still waiting on its id joins the held summary.
+    if let Some(item) = state.response_reasoning.get_mut(&index)
+        && !item.started
+        && !item.pending_text.is_empty()
+    {
+        item.pending_text.push_str(&text);
+        return Vec::new();
+    }
     // An empty delta carries nothing to show and must not open a part that would never close.
     if text.is_empty() {
         return ensure_responses_reasoning_started(state, index);
@@ -1016,8 +1097,11 @@ fn encode_responses_tool_delta(
         let Some(name) = tool.name.clone() else {
             return out;
         };
+        // The call opens its item next; held reasoning opens first to keep its place.
+        out.extend(open_held_reasoning(state, None));
         let output_index = state.next_response_output_index;
         state.next_response_output_index += 1;
+        let tool = state.tool_states.entry(index).or_default();
         tool.response_output_index = Some(output_index);
         tool.response_item_id = Some(responses_item_id_from(&resp_id, "fc", output_index));
         tool.started = true;
diff --git a/crates/switchyard-translation/src/codecs/stream.rs b/crates/switchyard-translation/src/codecs/stream.rs
index 87da2d649..db83015a7 100644
--- a/crates/switchyard-translation/src/codecs/stream.rs
+++ b/crates/switchyard-translation/src/codecs/stream.rs
@@ -109,6 +109,10 @@ pub(crate) struct ResponseReasoningState {
     pub(crate) encrypted: Option<String>,
     #[serde(default)]
     pub(crate) anthropic_signature: Option<String>,
+    /// Summary text held back while the item's provider id is still unknown. The item opens
+    /// once that id arrives, or once later output shows none is coming.
+    #[serde(default)]
+    pub(crate) pending_text: String,
 }
 
 // Tracks an in-progress streamed tool call across provider-specific deltas.
diff --git a/crates/switchyard-translation/tests/stream_translation.rs b/crates/switchyard-translation/tests/stream_translation.rs
index 01e9cc0da..6869e4545 100644
--- a/crates/switchyard-translation/tests/stream_translation.rs
+++ b/crates/switchyard-translation/tests/stream_translation.rs
@@ -1277,6 +1277,218 @@ fn openai_chat_stream_uses_summary_when_detail_text_is_empty() -> TestResult {
     Ok(())
 }
 
+// A Chat `reasoning_details` stream may send summary text before the id of the item it
+// belongs to. The Responses encoder must not open the item under a synthesized id, because the
+// encrypted payload that follows binds only to the provider's id. It holds the summary until
+// that id arrives, or until later output shows none is coming, and it takes the id from a
+// summary detail that carries one.
+#[test]
+fn openai_chat_stream_summary_before_id_keeps_reasoning_id_and_payload() -> TestResult {
+    let engine = TranslationEngine::default();
+    let chunk = |delta: Value, finish_reason: Option<&str>| {
+        json!({
+            "id": "chatcmpl-reasoning",
+            "object": "chat.completion.chunk",
+            "model": REASONING_MODEL,
+            "choices": [{"index": 0, "delta": delta, "finish_reason": finish_reason}]
+        })
+    };
+    let summary = |id: Option<&str>| {
+        let mut detail = json!({"type": "reasoning.summary", "summary": "summary first"});
+        if let Some(id) = id {
+            detail["id"] = json!(id);
+        }
+        json!({"reasoning_details": [detail]})
+    };
+    let encrypted = json!({"reasoning_details": [{
+        "type": "reasoning.encrypted", "id": "rs_provider", "data": "opaque-stream"
+    }]});
+    // Translates each delta as its own chunk and returns the events per chunk, then the
+    // events of the stop chunk and of finishing the stream.
+    let translate =
+        |deltas: Vec<Value>| -> Result<Vec<Vec<Value>>, Box<dyn std::error::Error + Send + Sync>> {
+            let mut state =
+                StreamTranslationState::new(WireFormat::OpenAiChat, WireFormat::OpenAiResponses);
+            let mut batches = Vec::new();
+            for (delta, finish_reason) in deltas
+                .into_iter()
+                .map(|delta| (delta, None))
+                .chain([(json!({}), Some("stop"))])
+            {
+                batches.push(engine.translate_event(
+                    &mut state,
+                    WireFormat::OpenAiChat,
+                    WireFormat::OpenAiResponses,
+                    &chunk(delta, finish_reason),
+                )?);
+            }
+            batches.push(engine.finish_stream(&mut state, WireFormat::OpenAiResponses)?);
+            Ok(batches)
+        };
+    let types = |batch: &[Value]| -> Vec<String> {
+        batch
+            .iter()
+            .filter_map(|event| event["type"].as_str().map(ToOwned::to_owned))
+            .collect()
+    };
+    let final_reasoning = |batches: &[Vec<Value>]| -> Result<Value, &'static str> {
+        batches
+            .iter()
+            .flatten()
+            .find(|event| event["type"] == "response.completed")
+            .and_then(|event| event["response"]["output"].as_array())
+            .and_then(|output| output.iter().find(|item| item["type"] == "reasoning"))
+            .cloned()
+            .ok_or("expected a reasoning item in the completed output")
+    };
+    let opened = [
+        "response.output_item.added",
+        "response.reasoning_summary_part.added",
+        "response.reasoning_summary_text.delta",
+    ];
+    let expected = json!({
+        "type": "reasoning",
+        "id": "rs_provider",
+        "status": "completed",
+        "summary": [{"type": "summary_text", "text": "summary first"}],
+        "encrypted_content": "opaque-stream",
+    });
+
+    // Summary before the id: the item waits, then opens under the id the payload names.
+    let batches = translate(vec![
+        json!({"role": "assistant"}),
+        summary(None),
+        encrypted.clone(),
+    ])?;
+    assert_eq!(types(&batches[1]), Vec::<String>::new());
+    assert_eq!(types(&batches[2]), opened);
+    assert_eq!(final_reasoning(&batches)?, expected);
+    for event in batches.iter().flatten().filter(|event| {
+        event["type"]
+            .as_str()
+            .is_some_and(|kind| kind.starts_with("response.reasoning_summary"))
+    }) {
+        assert_eq!(event["item_id"], "rs_provider", "{event}");
+    }
+
+    // Summary carrying the id: the item opens at once under it and the payload still attaches.
+    let batches = translate(vec![
+        json!({"role": "assistant"}),
+        summary(Some("rs_provider")),
+        encrypted,
+    ])?;
+    assert_eq!(types(&batches[1]), opened);
+    assert_eq!(batches[1][0]["item"]["id"], "rs_provider");
+    assert_eq!(final_reasoning(&batches)?, expected);
+
+    // No id ever comes: the answer opens the held item, under a synthesized id, ahead of itself.
+    let batches = translate(vec![
+        json!({"role": "assistant"}),
+        summary(None),
+        json!({"content": "answer"}),
+    ])?;
+    let opened_items: Vec<&str> = batches
+        .iter()
+        .flatten()
+        .filter(|event| event["type"] == "response.output_item.added")
+        .filter_map(|event| event["item"]["type"].as_str())
+        .collect();
+    assert_eq!(opened_items, ["reasoning", "message"]);
+    let reasoning = final_reasoning(&batches)?;
+    assert_eq!(
+        reasoning["summary"],
+        json!([{"type": "summary_text", "text": "summary first"}])
+    );
+    assert!(
+        reasoning["id"]
+            .as_str()
+            .is_some_and(|id| id.starts_with("rs_")),
+        "{reasoning}"
+    );
+    assert!(reasoning.get("encrypted_content").is_none(), "{reasoning}");
+    Ok(())
+}
+
+// A held summary opens ahead of any later item. A tool delta that carries only an id emits no
+// item yet, so it leaves the summary held; a reasoning item at a later index opens the held one
+// first, under a synthesized id, so the output keeps stream order.
+#[test]
+fn responses_stream_held_reasoning_opens_ahead_of_later_items() -> TestResult {
+    let engine = TranslationEngine::default();
+    let format = WireFormat::OpenAiResponses;
+    let mut state = StreamTranslationState::new(format, format);
+    let mut events = engine.encode_stream_event(
+        &mut state,
+        format,
+        LlmResponseStreamEvent::new(vec![
+            LlmResponseChunk::MessageStart {
+                id: Some("resp_1".into()),
+                model: Some(REASONING_MODEL.into()),
+            },
+            LlmResponseChunk::ReasoningDetailsDelta {
+                index: 0,
+                details: vec![json!({"type": "reasoning.summary", "summary": "held"})],
+                text: "held".into(),
+            },
+            LlmResponseChunk::ToolCallDelta {
+                index: 1,
+                id: Some("call_1".into()),
+                name: None,
+                arguments_delta: None,
+            },
+        ]),
+    )?;
+    assert!(
+        events
+            .iter()
+            .all(|event| event["type"] != "response.output_item.added"),
+        "{events:?}"
+    );
+    events.extend(engine.encode_stream_event(
+        &mut state,
+        format,
+        LlmResponseStreamEvent::new(vec![LlmResponseChunk::ReasoningDetailsDelta {
+            index: 2,
+            details: vec![json!({"type": "reasoning.encrypted", "id": "rs_2", "data": "opaque"})],
+            text: String::new(),
+        }]),
+    )?);
+    events.extend(engine.finish_stream(&mut state, format)?);
+
+    let added: Vec<(u64, &str)> = events
+        .iter()
+        .filter(|event| event["type"] == "response.output_item.added")
+        .map(|event| {
+            (
+                event["output_index"].as_u64().unwrap_or(u64::MAX),
+                event["item"]["id"].as_str().unwrap_or_default(),
+            )
+        })
+        .collect();
+    assert_eq!(added.len(), 2, "{added:?}");
+    assert_eq!(added[0].0, 0);
+    assert!(
+        added[0].1.starts_with("rs_") && added[0].1 != "rs_2",
+        "{added:?}"
+    );
+    assert_eq!(added[1], (1, "rs_2"));
+    let completed = events
+        .iter()
+        .find(|event| event["type"] == "response.completed")
+        .ok_or("expected response.completed")?;
+    let output = completed["response"]["output"]
+        .as_array()
+        .ok_or("output should be an array")?;
+    assert_eq!(output.len(), 2, "{output:?}");
+    assert_eq!(
+        output[0]["summary"],
+        json!([{"type": "summary_text", "text": "held"}])
+    );
+    assert_eq!(output[1]["id"], "rs_2");
+    assert_eq!(output[1]["encrypted_content"], "opaque");
+    Ok(())
+}
+
 // Verifies Anthropic thinking deltas become OpenAI reasoning_content, not content.
 #[test]
 fn anthropic_thinking_stream_deltas_do_not_become_openai_chat_content() -> TestResult {