{
  "api_version": "1",
  "updated": "2026-11-10",
  "latest_event": "2026-11-09",
  "rights": "© Frontier Log, all rights reserved.",
  "story": {
    "slug": "is-claude-opus-5-5-nerfed",
    "title": "Is Claude Opus 5.5 Nerfed?",
    "description": "An X post dated a shift in Opus 5.5 to Nov 3. Anthropic didn't announce a model change then. Claude Code updates came 16.5 hours before it and 6 hours after.",
    "url": "https://frontierlog.ai/stories/is-claude-opus-5-5-nerfed",
    "date": "2026-11-09",
    "image": "https://frontierlog.ai/og/story-is-claude-opus-5-5-nerfed.png",
    "event": "2026-09-22-claude-opus-5-5",
    "tags": [
      "coding-agents",
      "reasoning"
    ],
    "steps": [],
    "tables": [],
    "records": [
      {
        "date": "2026-09-22",
        "party": "Anthropic",
        "what": "launches Claude Opus 5.5, with medium as its default effort",
        "by": "Anthropic",
        "source": "https://www.anthropic.com/claude-opus-5-5",
        "quote": "At default effort (medium), Opus 5.5 scores 54.6%, higher than all other models"
      },
      {
        "date": "2026-09-22",
        "party": "Anthropic",
        "what": "releases Claude Code 2.1.280, which adds Opus 5.5 at its default effort",
        "by": "Claude Code on GitHub",
        "source": "https://github.com/anthropics/claude-code/releases/tag/v2.1.280",
        "quote": "Changed an effort level saved before `/effort` became per-model to no longer apply to newly released models such as Opus 5.5; they start at their default until you pick a level"
      },
      {
        "date": "2026-10-30",
        "party": "Anthropic",
        "what": "releases Claude Code 2.1.314 at 01:06 UTC",
        "by": "Claude Code on GitHub",
        "source": "https://github.com/anthropics/claude-code/releases/tag/v2.1.314",
        "quote": "Fixed sessions failing turn after turn with \"Invalid effort level\" when an organization's admin caps a model's effort: Claude Code now lowers the effort, retries, and says which level it uses"
      },
      {
        "date": "2026-10-31",
        "party": "Anthropic",
        "what": "releases Claude Code 2.1.316 at 01:01 UTC",
        "by": "Claude Code on GitHub",
        "source": "https://github.com/anthropics/claude-code/releases/tag/v2.1.316",
        "quote": "Added `CLAUDE_CODE_SUBAGENT_EFFORT` to set the effort level subagents run at when nothing else names one, instead of inheriting the session's"
      },
      {
        "date": "2026-11-03",
        "party": "Anthropic",
        "what": "releases Claude Code 2.1.317 at 01:25 UTC",
        "by": "Claude Code on GitHub",
        "source": "https://github.com/anthropics/claude-code/releases/tag/v2.1.317",
        "quote": "Changed subagents and teammates on a different model from the main conversation to use that model's saved effort level or its default, instead of the session's effort level",
        "key": true
      },
      {
        "date": "2026-11-04",
        "party": "Anthropic",
        "what": "releases Claude Code 2.1.318 at 00:01 UTC",
        "by": "Claude Code on GitHub",
        "source": "https://github.com/anthropics/claude-code/releases/tag/v2.1.318",
        "quote": "Removed the 2.1.288 fix that kept the model's earlier thinking when resuming a conversation started on 2.1.286 or earlier; that thinking can now be dropped",
        "key": true
      }
    ],
    "cites": [
      {
        "url": "https://www.anthropic.com/claude-opus-5-5",
        "by": "Anthropic",
        "medium": "launch post",
        "date": "2026-09-22"
      },
      {
        "url": "https://platform.claude.com/docs/en/release-notes/overview",
        "by": "Claude Platform Docs",
        "medium": "API release notes, read Nov 9"
      },
      {
        "url": "https://platform.claude.com/docs/en/build-with-claude/effort",
        "by": "Claude Platform Docs",
        "medium": "effort docs, read Nov 9"
      },
      {
        "url": "https://code.claude.com/docs/en/model-config",
        "by": "Claude Code Docs",
        "medium": "model configuration docs, read Nov 9"
      },
      {
        "url": "https://status.claude.com/history",
        "by": "Claude Status",
        "medium": "incident history, read Nov 9"
      },
      {
        "url": "https://platform.claude.com/docs/en/release-notes/system-prompts/claude-opus-5-5",
        "by": "Claude Platform Docs",
        "medium": "Claude Opus 5.5 system prompts, read Nov 9"
      },
      {
        "url": "https://x.com/shanemelaugh/status/2119192075505893695",
        "by": "@shanemelaugh",
        "medium": "X post",
        "date": "2026-11-07"
      },
      {
        "url": "https://github.com/anthropics/claude-code/releases/tag/v2.1.280",
        "by": "Claude Code on GitHub",
        "medium": "release v2.1.280",
        "date": "2026-09-22"
      },
      {
        "url": "https://github.com/anthropics/claude-code/releases/tag/v2.1.314",
        "by": "Claude Code on GitHub",
        "medium": "release v2.1.314",
        "date": "2026-10-30"
      },
      {
        "url": "https://github.com/anthropics/claude-code/releases/tag/v2.1.316",
        "by": "Claude Code on GitHub",
        "medium": "release v2.1.316",
        "date": "2026-10-31"
      },
      {
        "url": "https://github.com/anthropics/claude-code/releases/tag/v2.1.317",
        "by": "Claude Code on GitHub",
        "medium": "release v2.1.317",
        "date": "2026-11-03"
      },
      {
        "url": "https://github.com/anthropics/claude-code/releases/tag/v2.1.318",
        "by": "Claude Code on GitHub",
        "medium": "release v2.1.318",
        "date": "2026-11-04"
      }
    ],
    "sources": [
      "https://www.anthropic.com/claude-opus-5-5",
      "https://platform.claude.com/docs/en/release-notes/overview",
      "https://platform.claude.com/docs/en/build-with-claude/effort",
      "https://code.claude.com/docs/en/model-config",
      "https://status.claude.com/history",
      "https://platform.claude.com/docs/en/release-notes/system-prompts/claude-opus-5-5",
      "https://x.com/shanemelaugh/status/2119192075505893695",
      "https://github.com/anthropics/claude-code/releases/tag/v2.1.280",
      "https://github.com/anthropics/claude-code/releases/tag/v2.1.314",
      "https://github.com/anthropics/claude-code/releases/tag/v2.1.316",
      "https://github.com/anthropics/claude-code/releases/tag/v2.1.317",
      "https://github.com/anthropics/claude-code/releases/tag/v2.1.318"
    ],
    "updates": [],
    "body": [
      {
        "figure": "main"
      },
      {
        "p": "An [X post on Nov 7](https://x.com/shanemelaugh/status/2119192075505893695) by @shanemelaugh asked “is Opus 5.5 nerfed?” It said Gemini 4 Argon had analyzed 1,400 Claude Code sessions and found a sharp turn in how Claude Opus 5.5 reasons. Its chart dates the shift to Nov 3 at about 18:00 UTC, with the same model ID and the same Claude Code version. The chart says “the shift appeared mid-session across 7 active sessions”, and that visible summaries show “a behavior shift, not proof of changed model weights.” Anthropic's own dated records don't show a change to Opus 5.5 at that time. One Claude Code release came about 16.5 hours before that time. The next came about 6 hours after it."
      },
      {
        "h": "Medium effort since launch"
      },
      {
        "p": "Medium has been the default effort of [Claude Opus 5.5](https://frontierlog.ai/model/claude-opus-5-5) since Anthropic [launched it on Sep 22](https://www.anthropic.com/claude-opus-5-5). The launch post reports its scores “at default effort (medium)”. Anthropic's [effort docs](https://platform.claude.com/docs/en/build-with-claude/effort) say that most Claude models default to high. They add that “Claude Opus 5.5 and Claude Haiku 5.5 default to medium.” Claude Code added Opus 5.5 the same day in [version 2.1.280](https://github.com/anthropics/claude-code/releases/tag/v2.1.280). Its notes say new models like Opus 5.5 “start at their default until you pick a level”. Claude Code's [model configuration docs](https://code.claude.com/docs/en/model-config) still say that Opus 5.5 starts at medium."
      },
      {
        "h": "Two Claude Code releases around Nov 3"
      },
      {
        "p": "Anthropic released [Claude Code 2.1.317](https://github.com/anthropics/claude-code/releases/tag/v2.1.317) on GitHub on Nov 3 at 01:25 UTC. One of its changes concerns subagents and teammates that run on a different model from the main conversation. They now use “that model's saved effort level or its default, instead of the session's effort level.” The same release fixed a project's effort setting being ignored in sessions that an app starts ahead of time."
      },
      {
        "p": "[Claude Code 2.1.318](https://github.com/anthropics/claude-code/releases/tag/v2.1.318) followed on Nov 4 at 00:01 UTC. It removed an earlier fix for conversations started on version 2.1.286 or earlier. That fix had kept the model's earlier thinking when such a conversation was resumed. The release says “that thinking can now be dropped.” Several Claude Code releases in late October also changed how it handles effort. Among them are [2.1.314](https://github.com/anthropics/claude-code/releases/tag/v2.1.314) on Oct 30 and [2.1.316](https://github.com/anthropics/claude-code/releases/tag/v2.1.316) on Oct 31. The Oct 31 release added a setting for the effort level of subagents."
      },
      {
        "h": "No Opus 5.5 change in the release notes"
      },
      {
        "p": "The Claude [API release notes](https://platform.claude.com/docs/en/release-notes/overview) list entries on Nov 2, Nov 3 and Nov 5. None of them changes Opus 5.5. The Nov 3 entry adds Anthropic's text watermark to Claude Mythos 5, Claude Opus 4.7 and Claude Sonnet 4.6. Since the launch, the notes mention Opus 5.5 only in entries about fast mode and Dreams. Anthropic's [status page](https://status.claude.com/history) doesn't list an incident between Oct 31 and Nov 7."
      },
      {
        "p": "Anthropic also publishes the [system prompt](https://platform.claude.com/docs/en/release-notes/system-prompts/claude-opus-5-5) that Opus 5.5 runs with in the Claude apps on the web, iOS and Android. That page lists two versions, dated Sep 22 and Oct 27, and none from November. The Oct 27 version updated the list of Anthropic's products and models and added guidance on several sensitive topics. It doesn't mention the effort setting or how the model shows its thinking. The page covers the Claude apps, not Claude Code."
      },
      {
        "p": "Anthropic's records don't say what changed in the sessions the post describes."
      }
    ],
    "events": [
      "2026-09-22-claude-opus-5-5"
    ],
    "stories": [],
    "models": [
      "claude-opus-5-5"
    ]
  }
}