Bug Description

OpenClaw strips the anthropic-beta: max-model-output-200k-2025-02-19 (context1m) header when the Anthropic auth profile uses OAuth token mode (mode: token). The log emits:

ignoring context1m for OAuth token auth on anthropic/claude-opus-4-6; Anthropic rejects context-1m beta with OAuth auth

This fires on every single request, regardless of model or context size.

Impact

• Users on the Anthropic Max plan who authenticate via OAuth tokens cannot use extended context (>200K), even though their plan supports it.
• Under Anthropic API stress/enforcement periods, these requests may be rate-limited or rejected more aggressively because they lack the proper beta header.
• The warning fires continuously in logs (every few seconds during active sessions), creating log noise.
• Sessions that build up context over time hit 429 rate limits and become unresponsive, requiring manual session store deletion to recover.

Environment

• OpenClaw version: 2026.3.13 (61d171a) — also confirmed present in 2026.3.28
• OS: macOS (Darwin arm64)
• Node: v22.22.0
• Auth config:

{
  "auth": {
    "profiles": {
      "anthropic:manual": {
        "provider": "anthropic",
        "mode": "token"
      }
    }
  }
}

• Model: anthropic/claude-opus-4-6 (also fires for claude-sonnet-4-6)
• Plan: Anthropic Max (supports extended context)

Expected Behavior

The context1m beta header should be sent for OAuth token auth users, or at minimum there should be a config override (e.g., forceContext1m: true or anthropicBeta: ["max-model-output-200k-2025-02-19"]) that allows Max plan users to opt in.

Actual Behavior

The header is unconditionally stripped for all OAuth token auth profiles. No config override exists.

Reproduction

1. Configure Anthropic provider with mode: token (OAuth)
2. Start a session and send any message
3. Observe the warning in logs: ignoring context1m for OAuth token auth
4. As the session grows in context, requests begin hitting 429 rate limits
5. Eventually the session becomes unresponsive — only recoverable by deleting sessions.json and restarting

Suggested Fix

Either:

1. Pass the context1m header through for OAuth token auth (Anthropic's API may now accept it for Max plan tokens)
2. Add a provider-level config option to force the beta header regardless of auth mode
3. Add an auth profile flag like context1m: true that overrides the stripping behavior

Workaround

Delete ~/.openclaw/agents/main/sessions/sessions.json and restart the gateway when sessions become unresponsive. This is not sustainable for production use.