advisor-middleware

Anthropic's Advisor Strategy as a drop-in DeepAgents middleware.

Problem • How it works • Quick start • Configuration • Benchmark

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Open-source implementation of Anthropic's Advisor Strategy — a pattern that pairs a fast, cheap executor model with a powerful advisor model. The executor runs end-to-end; the advisor is consulted only on critical decisions. Result: better performance at lower cost.

advisor-middleware makes this a single import for DeepAgents. It handles provider detection, native API routing, fallback invocation, cost guardrails, and context curation — so you just plug it in and your agents get smarter.

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The Problem

Traditional sub-agent pattern	Advisor Strategy
Large orchestrator decomposes work into tasks	Small executor drives end-to-end
Expensive model runs every turn	Expensive model consulted only when needed
Worker pools + orchestration overhead	Zero orchestration — just a tool call
Hard to predict costs	max_uses guardrail caps advisor spend

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How It Works

flowchart TD
    A["Executor (Sonnet/Haiku)"] -->|"Runs every turn"| B{"Stuck on a\nhard decision?"}
    B -->|No| C["Continue executing\n(read, write, search, execute)"]
    C --> A
    B -->|Yes| D["Call advisor tool"]
    D --> E["Advisor (Opus)\nReviews shared context"]
    E -->|"Returns plan/correction/stop"| F["Executor resumes\nwith guidance"]
    F --> A

    style A fill:#fff,stroke:#333,color:#333
    style E fill:#c0392b,color:#fff
    style C fill:#2d6a4f,color:#fff
    style F fill:#2d6a4f,color:#fff

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The middleware operates in two modes depending on the executor's provider:

• Native mode (Anthropic executor): Injects the advisor_20260301 server-side tool spec. The API handles everything internally — zero extra round-trips, zero overhead on simple turns.
• Fallback mode (any provider): Exposes an advisor tool backed by a direct LLM call to the advisor model. Works with any executor/advisor combination.

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Quick Start

Install

pip install advisor-middleware

# Or from source
pip install git+https://github.com/emanueleielo/advisor-middleware.git

Minimal — zero config

from deepagents import create_deep_agent
from advisor_middleware import AdvisorMiddleware

mw = AdvisorMiddleware(advisor_model="claude-opus-4-6")

agent = create_deep_agent(
    model="anthropic:claude-sonnet-4-6",
    system_prompt="You are a senior software engineer.",
    backend=backend,
    middleware=[mw],
)

That's it. Sonnet executes, Opus advises. The middleware auto-detects Anthropic and uses the native API tool — no extra configuration needed.

Cross-provider

from advisor_middleware import AdvisorMiddleware, AdvisorConfig

mw = AdvisorMiddleware(
    config=AdvisorConfig(
        advisor_model="anthropic:claude-opus-4-6",
        prefer_native=False,  # force fallback mode
        max_uses_per_turn=2,
    ),
)

agent = create_deep_agent(
    model="openai:gpt-4o",  # any provider as executor
    middleware=[mw],
)

With compact-middleware

from advisor_middleware import AdvisorMiddleware
from compact_middleware import CompactionMiddleware, CompactionToolMiddleware

advisor_mw = AdvisorMiddleware(advisor_model="claude-opus-4-6")
compact_mw = CompactionMiddleware(model="anthropic:claude-sonnet-4-6", backend=backend)
compact_tool_mw = CompactionToolMiddleware(compact_mw)

agent = create_deep_agent(
    model="anthropic:claude-sonnet-4-6",
    backend=backend,
    middleware=[advisor_mw, compact_mw, compact_tool_mw],
)

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Configuration

AdvisorConfig

Parameter	Type	Default	Description
advisor_model	str | BaseChatModel	"claude-opus-4-6"	Advisor model ID or resolved instance
max_uses_per_turn	int	3	Max advisor calls per agent turn
max_uses_per_session	int | None	None	Lifetime cap (None = unlimited)
prefer_native	bool	True	Use native advisor_20260301 when possible
max_tokens	int	1024	Max tokens the advisor can generate per consultation
temperature	float	1.0	Advisor temperature (fallback mode only)
advisor_system_prompt	str | None	None	Override advisor prompt (fallback only)
context	ContextCurationConfig	(see below)	Controls context forwarded to advisor

ContextCurationConfig

Parameter	Type	Default	Description
include_system_prompt	bool	True	Forward executor's system prompt
include_tool_results	bool	True	Include tool results in context
max_context_messages	int | None	None	Limit messages sent to advisor
max_context_chars	int | None	None	Hard character budget for context

Cost control example

config = AdvisorConfig(
    max_uses_per_turn=2,        # max 2 consultations per turn
    max_uses_per_session=10,    # max 10 total in the session
    context=ContextCurationConfig(
        max_context_messages=10,  # only last 10 messages
        include_tool_results=False,  # skip bulky tool outputs
    ),
)

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Native vs Fallback

	Native (advisor_20260301)	Fallback (LLM call)
When	Anthropic executor + prefer_native=True	Any other executor, or prefer_native=False
How	Server-side tool spec injected into API call	Direct LLM call to advisor model
Round-trips	0 extra (handled by API)	1 per consultation
Overhead	Zero on simple turns	Minimal (only when called)
Model freedom	Anthropic advisor only	Any model as advisor
Context curation	Handled by API	Configurable via ContextCurationConfig

The middleware auto-detects the executor's provider and routes accordingly. You can force fallback mode with prefer_native=False for full control over context curation.

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Benchmark

We tested with a real debugging task: a 4-file async task queue system (connection pool + circuit breaker + rate limiter + retry logic) with interacting bugs that cause tasks to be silently dropped under load. The agent must read all files, diagnose cross-component interactions, and fix every bug.

python examples/benchmark.py

Results: Haiku solo vs Haiku + Opus Advisor

	Haiku Solo	Haiku + Opus Advisor
Tests passing	11/12	12/12
Turns	11	6
File writes	7 (3 rewrites)	3 (all correct first try)
Advisor calls	0	1
Duration	210.7s	90.3s

What happened: Haiku solo rewrote connection.py four times, going in circles trying to fix the semaphore leak. It never solved the circuit breaker recovery issue.

Haiku + Advisor consulted Opus once after reading all files. Opus confirmed the bug diagnosis, corrected a proposed fix, and flagged an issue Haiku missed. Haiku then wrote all three fixes correctly on the first attempt.

Why it works

The advisor doesn't help on simple tasks — Haiku handles routine reads, writes, and obvious fixes alone. The value shows on cross-file reasoning where Haiku gets stuck in trial-and-error loops:

• Opus identified that a semaphore release was needed for each discarded connection, not just one
• Opus correctly noted the circuit breaker race condition is a non-issue under asyncio's GIL (avoiding an unnecessary lock)
• Opus flagged that rate-limit timeouts should requeue tasks without consuming retry attempts

One well-timed consultation eliminated multiple cycles of incorrect rewrites.

Anthropic's benchmarks

From the original blog post:

Config	SWE-bench Multilingual	Cost per task
Sonnet + Opus Advisor	+2.7pp vs Sonnet solo	-11.9%
Haiku + Opus Advisor (BrowseComp)	41.2% vs 19.7% solo	85% cheaper than Sonnet

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Introspection

Track advisor usage programmatically:

mw = AdvisorMiddleware(advisor_model="claude-opus-4-6")

# ... after agent execution ...

print(f"Total consultations: {mw.get_total_uses()}")
print(f"Total advisor tokens: {mw.get_total_advisor_tokens()}")

for event in mw.get_events():
    print(f"  Turn {event['turn']}: {event['strategy']} — {event['advisor_tokens']} tokens")
    print(f"    Q: {event['question'][:80]}...")
    print(f"    A: {event['advice'][:80]}...")

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Architecture

advisor_middleware/
├── __init__.py        # Public API: AdvisorMiddleware, AdvisorConfig, ...
├── middleware.py       # Core middleware — dual-mode wrap_model_call
├── config.py          # AdvisorConfig + ContextCurationConfig dataclasses
├── state.py           # AdvisorState + AdvisorEvent TypedDicts
├── prompts.py         # Executor + advisor system prompts
├── providers.py       # Provider detection, native spec, fallback invocation
└── py.typed           # PEP 561 type marker

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Development

# Install with dev dependencies
pip install -e ".[dev,deepagents,anthropic]"

# Run tests
pytest

# Lint
ruff check advisor_middleware/

# Type check
mypy advisor_middleware/

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License

MIT — Emanuele Ielo