DeepSeek V4 Pro vs Flash in Code Fixes: Pro Wins on Precision

TheDeepArchive · reddit · 2026-08-14

Following a previous code analysis test, the author further compared DeepSeek V4 Pro (0813) and Flash (0731) on their ability to execute bug fixes.

Test Setup

Task: Execute an identical 15-item fix plan (covering P0/P1 issues like data loss and error handling) on the same base commit.
Verification: Comprehensive scoring via automated test suites, static analysis, and blind review by a third-party model.

Key Results

Mechanical Verification: Both models completed all 15 fixes without breaking existing tests. Pro added 20 regression tests with 0 new errors; Flash added 17 tests but introduced 1 new potential error in static analysis.
Blind Review: Pro scored a perfect 5 on correctness, demonstrating precise merge semantics and locking mechanisms. Flash (4) used an always-merge strategy that could mask data loss in specific scenarios.

This shows that while Flash is surprisingly good at finding issues, Pro remains more reliable for precise fixes and complex refactoring.

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