Claude Sonnet 4.5 vs ChatGPT 5.2: Hallucination Control and Fact-Checking Reliability

Hallucination control is one of the most critical dimensions of AI reliability in professional contexts, because errors rarely appear as obvious falsehoods and instead surface as plausible, well-structured, but incorrect assertions that can silently propagate into documents, decisions, or external communications.

In this comparison, Claude Sonnet 4.5 and ChatGPT 5.2 represent two distinct philosophies of factual reliability, one centered on preventive restraint, the other on productive approximation.

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Hallucinations are behavioral failures, not simple factual mistakes.

In real workflows, hallucinations rarely look like invented nonsense.

They emerge as overconfident completions, subtle assumption layering, or invented specificity introduced to make an answer feel complete.

This makes hallucination control less about raw accuracy and more about how a model behaves when certainty is low, incomplete, or contested.

A reliable system must therefore manage tone, scope, and refusal thresholds as carefully as factual recall.

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Common hallucination patterns in professional AI usage

Pattern	Description	Risk level
Plausible fabrication	Invented details that sound credible	High
Over-specific inference	Excessive detail beyond evidence	High
Confident uncertainty masking	Lack of hedging language	Medium
Silent assumption stacking	Implicit premises not disclosed	Medium
Source-less precision	Numbers or names without grounding	High

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Claude Sonnet 4.5 adopts a fact-safety-first completion strategy.

Claude Sonnet 4.5 demonstrates a conservative completion posture that actively prioritizes hallucination avoidance over output completeness.

When faced with ambiguous or under-specified prompts, it frequently slows its response, introduces explicit uncertainty markers, or refuses to speculate.

This behavior reduces the likelihood of fabricated facts, even at the cost of producing shorter or less assertive answers.

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Claude Sonnet 4.5 hallucination control behavior

Dimension	Observed behavior	Practical impact
Uncertainty signaling	Explicit and frequent	Low false confidence
Speculation tolerance	Very low	Reduced hallucinations
Refusal calibration	Conservative	Higher safety
Variance under paraphrasing	Low	Predictable outputs
Best fit	External-facing content	Compliance, documentation

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ChatGPT 5.2 favors informative continuity over strict restraint.

ChatGPT 5.2 is optimized for helpfulness and continuity, often attempting to complete an answer even when factual certainty is partial.

It uses internal reasoning and probabilistic inference to fill gaps, producing outputs that are coherent, structured, and often immediately usable.

This makes it powerful for drafting and exploration, but increases hallucination risk if outputs are treated as authoritative without verification.

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ChatGPT 5.2 hallucination behavior

Dimension	Observed behavior	Practical impact
Uncertainty signaling	Implicit unless prompted	Requires constraints
Speculation tolerance	Moderate	Higher productivity
Completion bias	Strong	Richer drafts
Variance under paraphrasing	Medium	Adaptive but less stable
Best fit	Internal analysis	Drafting, ideation

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Failure modes reveal deeper reliability differences.

The most meaningful distinction between the two systems emerges not when they succeed, but when they fail.

Claude Sonnet 4.5 tends to fail by withholding information, declining to answer where partial reasoning might still be acceptable.

ChatGPT 5.2 tends to fail by over-structuring uncertain reasoning, presenting inferred conclusions with persuasive clarity.

Both failure modes are rational, but they carry different professional risks.

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Failure mode comparison

Model	Typical failure	Resulting risk
Claude Sonnet 4.5	Excessive refusal	Lost insight
ChatGPT 5.2	Overconfident inference	Silent misinformation

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Fact-checking workflows align differently with each model.

In workflows where outputs are published, shared with clients, or incorporated into regulated documents, hallucination tolerance approaches zero.

In workflows where outputs are internal, iterative, or exploratory, some level of approximation can be acceptable if review follows.

Claude Sonnet aligns naturally with publish-first workflows.

ChatGPT aligns naturally with draft-first workflows.

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Model alignment by workflow type

Workflow type	Better alignment
Compliance documentation	Claude Sonnet 4.5
Client-facing content	Claude Sonnet 4.5
Internal research drafts	ChatGPT 5.2
Brainstorming and ideation	ChatGPT 5.2
First-pass summaries	ChatGPT 5.2

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Variance under rephrasing is a key reliability indicator.

When prompts are rephrased or slightly altered, Claude Sonnet 4.5 maintains consistent factual boundaries and tone.

ChatGPT 5.2 adapts more fluidly, sometimes shifting assumptions or levels of detail based on framing.

Low variance supports auditability.

Higher variance supports adaptability.

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Response stability under paraphrasing

Aspect	Claude Sonnet 4.5	ChatGPT 5.2
Factual boundary stability	High	Medium
Tone consistency	High	Variable
Assumption drift	Minimal	Possible
Audit suitability	Strong	Moderate

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Governance overhead differs significantly.

Claude Sonnet 4.5 reduces governance burden because its default behavior already aligns with conservative expectations.

ChatGPT 5.2 requires prompt discipline, review steps, and sometimes post-processing to ensure factual safety.

The trade-off is between built-in restraint and managed productivity.

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Governance implications

Model	Governance effort	Default safety
Claude Sonnet 4.5	Low	High
ChatGPT 5.2	Medium	Moderate

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Hallucination control reflects design philosophy, not intelligence limits.

Neither model hallucinates because it lacks capability.

They differ because they optimize for different definitions of usefulness.

Claude Sonnet 4.5 treats incorrect confidence as the primary failure.

ChatGPT 5.2 treats incomplete assistance as the primary failure.

Professional reliability emerges from choosing the failure mode that aligns with the risk tolerance of the task, not from assuming one approach is universally superior.

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