The new quantization branch only runs when `enable_schema` is true, so deployments that still run without schema support will never produce a `QuantizedSpann` segment even if the user explicitly sets `quantize = true` in the collection configuration. In that mode we still fall through to the legacy `if matches!(config.vector_index, VectorIndexConfiguration::Spann(_)) { vector_segment_type = SegmentType::Spann; }`, silently dropping the quantization flag and creating a plain Spann segment. That makes quantization impossible in non-schema environments.

To keep the behavior consistent, mirror this check for the configuration-only path and switch to `SegmentType::QuantizedSpann` whenever `InternalSpannConfiguration.quantize` is true:

```suggestion
                        if schema.get_internal_spann_config().is_some() {
                            // Use QuantizedSpann if quantization is enabled, otherwise use Spann
                            if schema.is_quantization_enabled() {
                                vector_segment_type = SegmentType::QuantizedSpann;
                            } else {
                                vector_segment_type = SegmentType::Spann;
                            }
                        }
                    }
                }
                if let Some(config) = configuration.as_ref() {
                    if let VectorIndexConfiguration::Spann(ref spann_cfg) = config.vector_index {
                        vector_segment_type = if spann_cfg.quantize {
                            SegmentType::QuantizedSpann
                        } else {
                            SegmentType::Spann
                        };
                    }
                }
```

(Adjust the existing branch below so it inspects `spann_cfg.quantize` instead of hard-coding `SegmentType::Spann`.)

File: rust/frontend/src/impls/service_based_frontend.rs
Line: 546