diff --git a/amplifier_module_provider_anthropic/_cost.py b/amplifier_module_provider_anthropic/_cost.py
index 88fbf73..bff060f 100644
--- a/amplifier_module_provider_anthropic/_cost.py
+++ b/amplifier_module_provider_anthropic/_cost.py
@@ -157,8 +157,14 @@
     },
     # ------------------------------------------------------------------
     # Claude Haiku 3.5  ($0.80 / $4.00 / $0.08 / $1.00)
+    #
+    # The served id is claude-3-5-haiku-20241022: Claude 3-generation ids put
+    # the version before the family, and later ids put the family first.
+    # "claude-haiku-3-5-20250929" was neither shape -- family-first ordering
+    # with Sonnet 4.5's snapshot date. `compute_cost` does an exact
+    # `_RATES.get()`, so the real id missed and Haiku 3.5 cost returned None.
     # ------------------------------------------------------------------
-    "claude-haiku-3-5-20250929": {
+    "claude-3-5-haiku-20241022": {
         "input_per_m": Decimal("0.80"),
         "output_per_m": Decimal("4.00"),
         "cache_read_per_m": Decimal("0.08"),
diff --git a/tests/test_cost.py b/tests/test_cost.py
index e6e8ada..b135902 100644
--- a/tests/test_cost.py
+++ b/tests/test_cost.py
@@ -146,6 +146,33 @@ def test_unknown_model_returns_none():
     assert result is None, f"Expected None for unknown model, got {result!r}"
 
 
+# ---------------------------------------------------------------------------
+# Haiku 3.5 is keyed by its served model id
+# ---------------------------------------------------------------------------
+def test_haiku_35_real_model_id_is_priced():
+    """The id the API actually returns must resolve to the Haiku 3.5 rates."""
+    result = compute_cost("claude-3-5-haiku-20241022", input_tokens=1_000_000)
+    assert result == Decimal("0.80")
+
+
+def test_haiku_35_output_and_cache_rates():
+    assert compute_cost(
+        "claude-3-5-haiku-20241022", output_tokens=1_000_000
+    ) == Decimal("4.00")
+    assert compute_cost(
+        "claude-3-5-haiku-20241022", cache_read_input_tokens=1_000_000
+    ) == Decimal("0.08")
+    assert compute_cost(
+        "claude-3-5-haiku-20241022", cache_creation_input_tokens=1_000_000
+    ) == Decimal("1.00")
+
+
+def test_former_haiku_35_key_was_never_a_served_model_id():
+    """No model was served as claude-haiku-3-5-20250929, so it must not price."""
+    result = compute_cost("claude-haiku-3-5-20250929", input_tokens=1_000_000)
+    assert result is None
+
+
 # ---------------------------------------------------------------------------
 # (g) None != Decimal('0'): unknown is distinct from free
 # ---------------------------------------------------------------------------