Source Intelligence
Sweep 28 Aug 2026 · 00:00Z Build v2.1.250 478 read Stable v2.1.236 Latest v2.1.250 Next v2.1.251 Feeds RSS JSON llms.txt
Reading a new release v2.1.251 Analysing changes · 2/5 Deeper second pass · 0/5 agents 427 findings $12.75 so far

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

One change

prompting-claude-opus-5

build-with-claude/prompt-engineering/prompting-claude-opus-5

first seen The page's own history The capture it came from

Nearest release: v2.1.246, published 3 hours after this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

build-with-claude/prompt-engineering/prompting-claude-opus-5 Changed · +2 / -2 lines

from line 9
 Claude Opus 5 is built for complex agentic coding and enterprise work, with particular strengths in long-horizon agentic tasks. It performs well out of the box on existing Claude Opus 4.8 prompts. The following patterns cover the behaviors that most often require tuning.
 
 <Note>
-  For API changes when migrating from Claude Opus 4.8 (thinking on by default, and disabling thinking capped at `high` effort), see the [migration guide](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5).
+  For API changes when migrating from Claude Opus 4.8 (thinking on by default, and disabling thinking capped at `high` effort), see the [migration guide](https://platform.claude.com/docs/en/models/opus-5/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5).
 </Note>
 
 ## Capability improvements
from line 92
 
 ## Running with thinking disabled
 
-Claude Opus 5 runs with [thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, and thinking can be disabled only at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below; see the [migration guide](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5). With thinking disabled, two artifacts can occasionally appear in the model's visible output. The primary mitigation for both is to keep thinking enabled and control token cost with lower effort levels instead of disabling thinking: for most tasks, thinking enabled at `low` effort performs better than thinking disabled at similar cost.
+Claude Opus 5 runs with [thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, and thinking can be disabled only at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below; see the [migration guide](https://platform.claude.com/docs/en/models/opus-5/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5). With thinking disabled, two artifacts can occasionally appear in the model's visible output. The primary mitigation for both is to keep thinking enabled and control token cost with lower effort levels instead of disabling thinking: for most tasks, thinking enabled at `low` effort performs better than thinking disabled at similar cost.
 
 **Tool calls as text.** With thinking disabled, the model occasionally writes a tool call into its user-facing text instead of emitting a structured `tool_use` block. The turn completes normally and the call never runs, and in agentic loops the leaked text stays in the conversation history, so later turns are affected as well. This is most common on tool-heavy workloads such as search.