1. Key Difference 1: Storage Architecture - Loki uses a log-based storage architecture where logs are stored as streams of events in an append-only manner. On the other hand, Seq uses a time-series storage architecture where events are stored in a time-ordered sequence, allowing for efficient retrieval based on time ranges.

2. Key Difference 2: Querying Capability - Loki offers log-based query language and allows users to query logs using labels, log lines, and time ranges. It provides powerful filtering and aggregation capabilities specifically designed for log analysis. Whereas, Seq offers a flexible query language allowing users to query structured log events or metrics. It supports SQL-like syntax and enables filtering, aggregating, and transforming log data.

3. Key Difference 3: Scalability - Loki is highly scalable due to its use of a distributed storage system like object storage. It can handle massive amounts of log data and can be horizontally scaled to meet growing needs. Conversely, Seq is not primarily designed for massive scalability and is more suitable for smaller-scale log storage and analysis requirements.

4. Key Difference 4: Data Retention - Loki has a built-in retention mechanism that allows users to define how long log data should be retained based on time or size. This feature helps in managing storage costs and compliance requirements. In contrast, Seq does not have built-in data retention capabilities and relies on external processes or scripts for managing data retention.

5. Key Difference 5: Integration with Logging Libraries - Loki integrates well with popular logging libraries like Promtail, Fluentd, and Logstash, making it easy to ingest logs into the system. In contrast, Seq integrates with various logging libraries but is mainly focused on ASP.NET Core logging and Serilog.

6. Key Difference 6: Cost Model - Loki follows a cost-effective model where users only pay for the storage used. Its ability to compress and store logs efficiently contributes to cost optimization. On the other hand, Seq follows a per-instance pricing model and requires licensing based on the number of Seq instances deployed.

In summary, Loki and Seq differ in their storage architecture, querying capability, scalability, data retention, integration with logging libraries, and cost model. Loki excels in log-based storage and analysis at scale, while Seq focuses more on structured log events and metrics with an emphasis on ASP.NET Core logging.