Head-to-head comparison
GPT-3.5 Turbo Instruct (OpenAI) and Sonar Reasoning Pro (Perplexity) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.
Snapshot as of 18 August 2026
As of 18 August 2026, Sonar Reasoning Pro holds the stronger ModelCap Index position (#109 vs #111); GPT-3.5 Turbo Instruct is 4× cheaper per output token ($2.00/1M vs $8.00/1M); and Sonar Reasoning Pro offers the longer context window (128K vs 4K tokens).
Evidence: publisher corpus prior · leave-one-anchor-out calibrated · 1 public benchmark observation across 1 board. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.
Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.
Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.
Sonar Reasoning Pro ranks higher on the ModelCap Index as of 18 August 2026: #109 against #111. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it.
GPT-3.5 Turbo Instruct is cheaper on output tokens: $2.00/1M against $8.00/1M. Input tokens are $1.50/1M for GPT-3.5 Turbo Instruct and $2.00/1M for Sonar Reasoning Pro. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens.
Sonar Reasoning Pro has the larger context window: 128K tokens against 4K.
The two models do not share a coding benchmark board on ModelCap yet, so no head-to-head coding score is published; the ModelCap Index position is the closest overall signal.
GPT-3.5 Turbo Instruct: API only. Sonar Reasoning Pro: API only. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.
ModelCap currently lists 1 API provider for GPT-3.5 Turbo Instruct and 1 for Sonar Reasoning Pro, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.
Every figure comes from the sealed ModelCap dataset published 18 August 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.