fix(bedrock): send context-1m-2025-08-07 beta so Opus 4.6/4.7 get 1M context (#16793)

On AWS Bedrock (and Azure AI Foundry), Claude Opus 4.6/4.7 and Sonnet 4.6
are capped at 200K context unless the request carries the
`context-1m-2025-08-07` beta header. On native Anthropic (api.anthropic.com)
1M went GA so the header is a harmless no-op, but Bedrock/Azure still gate
it as beta as of 2026-04.

Hermes was advertising 1M in model_metadata.py (`claude-opus-4-7: 1000000`)
while silently sending a request without the beta — so Bedrock users saw
a 200K ceiling with no error message, and no config knob unblocked it.
Claude Code sends this header by default, which is why the same Bedrock
credentials worked there.

- Add `context-1m-2025-08-07` to `_COMMON_BETAS` (alongside interleaved
  thinking and fine-grained tool streaming).
- Strip it in `_common_betas_for_base_url` for MiniMax bearer-auth
  endpoints — they host their own models, not Claude, so Anthropic beta
  headers are irrelevant and could risk rejection.
- Attach `_COMMON_BETAS` as `default_headers` on the AnthropicBedrock
  client. Previously that constructor passed no betas at all, so native
  Anthropic had the 1M unlock via default_headers but Bedrock didn't.
- Fast-mode per-request `extra_headers` already rebuilds from
  `_common_betas_for_base_url`, so it picks up the 1M beta automatically.

Reported by user 'Rodmar' on Discord: Bedrock Opus 4.7 stuck at 200K while
same credentials worked in Claude Code.

agent/anthropic_adapter.py

@@ -202,19 +202,33 @@ def _forbids_sampling_params(model: str) -> bool:
 
 
 # Beta headers for enhanced features (sent with ALL auth types).
-# As of Opus 4.7 (2026-04-16), both of these are GA on Claude 4.6+ — the
+# As of Opus 4.7 (2026-04-16), the first two are GA on Claude 4.6+ — the
 # beta headers are still accepted (harmless no-op) but not required. Kept
 # here so older Claude (4.5, 4.1) + third-party Anthropic-compat endpoints
 # that still gate on the headers continue to get the enhanced features.
-# Migration guide: remove these if you no longer support ≤4.5 models.
+#
+# ``context-1m-2025-08-07`` unlocks the 1M context window on Claude Opus 4.6/4.7
+# and Sonnet 4.6 when served via AWS Bedrock or Azure AI Foundry. 1M is GA on
+# native Anthropic (api.anthropic.com) for Opus 4.6+, but Bedrock/Azure still
+# gate it behind this beta header as of 2026-04 — without it Bedrock caps Opus
+# at 200K even though model_metadata.py advertises 1M. The header is a harmless
+# no-op on endpoints where 1M is GA.
+#
+# Migration guide: remove these if you no longer support ≤4.5 models or once
+# Bedrock/Azure promote 1M to GA.
 _COMMON_BETAS = [
     "interleaved-thinking-2025-05-14",
     "fine-grained-tool-streaming-2025-05-14",
+    "context-1m-2025-08-07",
 ]
 # MiniMax's Anthropic-compatible endpoints fail tool-use requests when
 # the fine-grained tool streaming beta is present.  Omit it so tool calls
 # fall back to the provider's default response path.
 _TOOL_STREAMING_BETA = "fine-grained-tool-streaming-2025-05-14"
+# 1M context beta — see comment on _COMMON_BETAS above. Stripped for
+# Bearer-auth (MiniMax) endpoints since they host their own models and
+# unknown Anthropic beta headers risk request rejection.
+_CONTEXT_1M_BETA = "context-1m-2025-08-07"
 
 # Fast mode beta — enables the ``speed: "fast"`` request parameter for
 # significantly higher output token throughput on Opus 4.6 (~2.5x).
@@ -357,9 +371,14 @@ def _common_betas_for_base_url(base_url: str | None) -> list[str]:
     that include Anthropic's ``fine-grained-tool-streaming`` beta — every
     tool-use message triggers a connection error.  Strip that beta for
     Bearer-auth endpoints while keeping all other betas intact.
+
+    The ``context-1m-2025-08-07`` beta is also stripped for Bearer-auth
+    endpoints — MiniMax hosts its own models, not Claude, so the header is
+    irrelevant at best and risks request rejection at worst.
     """
     if _requires_bearer_auth(base_url):
-        return [b for b in _COMMON_BETAS if b != _TOOL_STREAMING_BETA]
+        _stripped = {_TOOL_STREAMING_BETA, _CONTEXT_1M_BETA}
+        return [b for b in _COMMON_BETAS if b not in _stripped]
     return _COMMON_BETAS
 
 
@@ -456,6 +475,13 @@ def build_anthropic_bedrock_client(region: str):
     Claude feature parity: prompt caching, thinking budgets, adaptive
     thinking, fast mode — features not available via the Converse API.
 
+    Attaches the common Anthropic beta headers as client-level defaults so
+    that Bedrock-hosted Claude models get the same enhanced features as
+    native Anthropic. The ``context-1m-2025-08-07`` beta in particular
+    unlocks the 1M context window for Opus 4.6/4.7 on Bedrock — without
+    it, Bedrock caps these models at 200K even though the Anthropic API
+    serves them with 1M natively.
+
     Auth uses the boto3 default credential chain (IAM roles, SSO, env vars).
     """
     if _anthropic_sdk is None:
@@ -473,6 +499,7 @@ def build_anthropic_bedrock_client(region: str):
     return _anthropic_sdk.AnthropicBedrock(
         aws_region=region,
         timeout=Timeout(timeout=900.0, connect=10.0),
+        default_headers={"anthropic-beta": ",".join(_COMMON_BETAS)},
     )
 
 

tests/agent/test_bedrock_1m_context.py

@@ -0,0 +1,105 @@
+"""Tests for the 1M-context beta header on AWS Bedrock Claude models.
+
+Claude Opus 4.6/4.7 and Sonnet 4.6 support a 1M context window, but on AWS
+Bedrock (and Azure AI Foundry) that window is still gated behind the
+``context-1m-2025-08-07`` beta header as of 2026-04. Without it, Bedrock
+caps these models at 200K even though ``model_metadata.py`` advertises 1M.
+
+These tests guard the invariant that the header is always emitted on the
+Bedrock client path, and that it survives the MiniMax bearer-auth strip.
+"""
+
+from unittest.mock import MagicMock, patch
+
+
+class TestBedrockContext1MBeta:
+    """``context-1m-2025-08-07`` must reach Bedrock Claude requests."""
+
+    def test_common_betas_includes_1m(self):
+        from agent.anthropic_adapter import _COMMON_BETAS, _CONTEXT_1M_BETA
+
+        assert _CONTEXT_1M_BETA == "context-1m-2025-08-07"
+        assert _CONTEXT_1M_BETA in _COMMON_BETAS
+
+    def test_common_betas_for_native_anthropic_includes_1m(self):
+        """Native Anthropic endpoints (and Bedrock with empty base_url) get 1M."""
+        from agent.anthropic_adapter import (
+            _common_betas_for_base_url,
+            _CONTEXT_1M_BETA,
+        )
+
+        assert _CONTEXT_1M_BETA in _common_betas_for_base_url(None)
+        assert _CONTEXT_1M_BETA in _common_betas_for_base_url("")
+        assert _CONTEXT_1M_BETA in _common_betas_for_base_url(
+            "https://api.anthropic.com"
+        )
+
+    def test_common_betas_strips_1m_for_minimax(self):
+        """MiniMax bearer-auth endpoints host their own models — strip 1M beta."""
+        from agent.anthropic_adapter import (
+            _common_betas_for_base_url,
+            _CONTEXT_1M_BETA,
+        )
+
+        for url in (
+            "https://api.minimax.io/anthropic",
+            "https://api.minimaxi.com/anthropic",
+        ):
+            betas = _common_betas_for_base_url(url)
+            assert _CONTEXT_1M_BETA not in betas, (
+                f"1M beta must be stripped for MiniMax bearer endpoint {url}"
+            )
+            # Other betas still present
+            assert "interleaved-thinking-2025-05-14" in betas
+
+    def test_build_anthropic_bedrock_client_sends_1m_beta(self):
+        """AnthropicBedrock client must carry the 1M beta in default_headers.
+
+        This is the load-bearing assertion for the reported bug:
+        without this header Bedrock serves Opus 4.6/4.7 with a 200K cap.
+        """
+        import agent.anthropic_adapter as adapter
+
+        fake_sdk = MagicMock()
+        fake_sdk.AnthropicBedrock = MagicMock()
+
+        with patch.object(adapter, "_anthropic_sdk", fake_sdk):
+            adapter.build_anthropic_bedrock_client(region="us-west-2")
+
+        call_kwargs = fake_sdk.AnthropicBedrock.call_args.kwargs
+        assert call_kwargs["aws_region"] == "us-west-2"
+
+        default_headers = call_kwargs.get("default_headers") or {}
+        beta_header = default_headers.get("anthropic-beta", "")
+        assert "context-1m-2025-08-07" in beta_header, (
+            "Bedrock client must send context-1m-2025-08-07 or Opus 4.6/4.7 "
+            "silently caps at 200K context"
+        )
+        # Other common betas still present — no regression.
+        assert "interleaved-thinking-2025-05-14" in beta_header
+        assert "fine-grained-tool-streaming-2025-05-14" in beta_header
+
+    def test_build_anthropic_kwargs_includes_1m_for_bedrock_fastmode(self):
+        """Fast-mode requests (per-request extra_headers) still include 1M beta.
+
+        Per-request extra_headers override client-level default_headers, so
+        the fast-mode path must re-include everything in _COMMON_BETAS.
+        """
+        from agent.anthropic_adapter import build_anthropic_kwargs
+
+        kwargs = build_anthropic_kwargs(
+            model="claude-opus-4-7",
+            messages=[{"role": "user", "content": "hi"}],
+            tools=None,
+            max_tokens=1024,
+            reasoning_config=None,
+            is_oauth=False,
+            # Empty base_url mirrors AnthropicBedrock (no HTTP base URL)
+            base_url=None,
+            fast_mode=True,
+        )
+        beta_header = kwargs.get("extra_headers", {}).get("anthropic-beta", "")
+        assert "context-1m-2025-08-07" in beta_header, (
+            "fast-mode extra_headers must carry the 1M beta or it overrides "
+            "client-level default_headers and Bedrock drops back to 200K"
+        )