Much research has investigated students' metacognitive growth focusing on their metacognitive knowledge and metacognitive strategies as individual differences in learning to write in a second/foreign language (L2). Yet to date, changes in metacognitive experiences when learning to write, a subcategory of metacognition, have been insufficiently scrutinized. To bridge this gap, we employed a mixed-methods approach to examine learners' development in English as a foreign language (EFL), capturing their metacognitive experiences longitudinally. Specifically, we investigated the changes in 390 EFL learners' metacognitive experiences in writing and their writing development over one semester. A questionnaire was used to measure these learners' metacognitive experiences over two writing tasks, capturing metacognitive judgments, metacognitive feelings, online task-specific metacognitive knowledge, and online task-specific metacognitive strategies. We selected 12 participants for follow-up semi-structured interviews. We processed the quantitative data using Latent Profile Analysis (LPA) to identify these EFL learners' metacognitive experience profiles. Findings of LPA using Mplus 8.3 revealed two metacognitive experiences profiles, characterized by intensive and less intensive metacognitive experiences. Further quantitative analysis using paired samples t-tests in SPSS 24.0 indicated that EFL learners' metacognitive experiences changed in alignment with their writing development in terms of lexical complexity, syntactic complexity, fluency, and overall writing scores. Qualitative findings from thematic analysis using NVivo 12 identified two factors affecting the changes in EFL learners' metacognitive experiences, including their involvement in writing and development in linguistic competence. As is evident, the quantitative and qualitative findings point to a more nuanced and precise understanding of the changes in these EFL learners' metacognitive experiences in learning to write.