Quick Take

Thinking Machines’ Inkling (xhigh) and OpenAI’s GPT-5.3 Codex (xhigh) are both positioned as high-tier models. Released on July 15, 2026, Inkling focuses on efficiency and speed. OpenAI’s GPT-5.3 Codex, released earlier on February 5, 2026, emphasizes raw intelligence and comprehensive benchmark dominance.

Benchmark Read

GPT-5.3 Codex demonstrates a higher Intelligence index of 44.3 compared to Inkling’s 40.7. In specific benchmarks, GPT-5.3 Codex consistently leads:

• GPQA: 0.915 (GPT-5.3) vs 0.872 (Inkling)
• HLE: 0.399 (GPT-5.3) vs 0.297 (Inkling)
• SciCode: 0.532 (GPT-5.3) vs 0.461 (Inkling)
• LCR: 0.74 (GPT-5.3) vs 0.633 (Inkling)

Inkling provides a Coding index of 52.1, while the coding capability for GPT-5.3 Codex remains unknown. GPT-5.3 Codex also reports strong performance in specialized benchmarks like IFBench (0.754), TerminalBench Hard (0.530), and TAU2 (0.860).

Cost and Speed

There is a stark contrast in operational performance and pricing. Inkling is significantly more affordable for output-heavy tasks, costing $4.68/1M tokens compared to GPT-5.3 Codex’s $14.00/1M tokens.

Regarding speed, Inkling excels in latency, boasting a time-to-first-token of 1.597s, whereas GPT-5.3 Codex experiences a significantly longer delay of 67.017s. While GPT-5.3 Codex maintains a higher output speed of 95.367 tok/s compared to Inkling’s 82.899 tok/s, the initial latency makes Inkling feel much more responsive for real-time applications.

Best Fit

Inkling is best suited for developers building real-time applications where latency is critical and cost control is a primary concern. Its rapid time-to-first-token makes it ideal for conversational interfaces. GPT-5.3 Codex is the preferred choice for complex reasoning tasks, research, and applications where the highest possible intelligence and benchmark accuracy are required, regardless of the higher cost and latency.