[BUG] Claude consistently makes unverified technical assertions that cascade into incorrect development decisions

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude routinely states technical facts with high confidence based on training memory, without verifying against documentation, source code, or live tests. When these assertions are wrong, every downstream decision built on them is also wrong — leading to wasted work, incorrect implementations, or irreversible actions.

This is not an isolated incident. The pattern repeats:

1. User asks a technical question (version support, API behavior, architecture tradeoff)
2. Claude answers confidently from memory, with no hedging and no verification
3. User proceeds with development based on Claude's answer
4. Later: the answer was wrong — but by then, code has been written, data has been deleted, or hours have been spent in the wrong direction

Concrete examples from one session:

• Claude stated "PostgreSQL 17 has native uuidv7()" → user wiped local database to upgrade → uuidv7() does not exist in PG 17 → irreversible data loss
• Claude then stated "Cloud SQL may not support PG 18" → false, PG 18 is Cloud SQL's default version
• Both wrong answers were stated with the same confident tone as correct ones — user had no signal to distrust either

Additional pattern to highlight:

Pattern 2: Premature conclusions during debugging (not covered in the original report)

During debugging sessions, Claude also frequently:

1. Skips reading logs or actual code before forming a conclusion
2. Immediately asserts a root cause without evidence
3. Proceeds to "fix" in the wrong direction based on that unverified conclusion
4. The actual bug is never fixed; instead, incorrect patches accumulate as technical debt

This wastes user time and tokens, and leaves the codebase in a worse state than before debugging started. The fix attempts create noise that makes the real problem harder to find later.

Both patterns share the same root cause: Claude treats "I believe X" as equivalent to "X is verified", and acts on that belief without pausing to check. The result in Pattern 1 is wrong architectural decisions; the result in Pattern 2 is a growing pile of incorrect patches around an unfound bug.

What Should Happen?

For verifiable technical claims (version support, API existence, cloud service capabilities), Claude should either:

1. Verify before stating (fetch docs, run a test), or
2. Explicitly flag as unverified: "I believe X but haven't confirmed — let me check before you act on this"

The current behavior — confident assertions with no verification signal — is actively harmful in a development context.

Error Messages/Logs

Steps to Reproduce

1. Ask Claude a version-specific technical question (e.g. "does PostgreSQL 17 support uuidv7()?")
2. Claude answers confidently: "Yes, PG 17 has native uuidv7()"
3. User authorizes destructive action based on that answer (e.g. wipe database, upgrade)
4. Discover Claude was wrong after irreversible action is taken

Claude Model

Opus 4.7 1M

Is this a regression?

No

Last Working Version

_No response_

Claude Code Version

2.1.132

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

The project CLAUDE.md already contains explicit rules: "未經驗證不要下結論" (no conclusions without verification). These rules are loaded every session. Claude acknowledges them, then violates them in the same response. The rule exists but the enforcement mechanism does not.

Claude has access to WebSearch and WebFetch tools that could verify these claims in seconds before stating them. The issue is that Claude defaults to answering from memory rather than treating "I don't know for certain" as a trigger to verify first.